1. Field of the Invention
The present invention relates to a system for containing and neutralizing heavy vapor clouds of corrosive and toxic substances, such as hydrogen fluoride (HF), hydrofluoric acid, ammonia, chlorine and the like. More particularly, the present invention relates to a system for containing and neutralizing such substances in the event of an accidental release.
2. Description of Prior Art
Hydrofluoric acid is toxic and corrosive. In gaseous vapor or liquid form, hydrofluoric acid attacks the skin, and will on contact cause ulceration of mucous membranes and possibly chemical pneumonia to those exposed to it. Hydrofluoric acid is, however, an industrially important chemical. It is used to manufacture fluorine and to prepare fluorides and other chemical compounds. It is also used as a catalyst for isomerization, condensation, polymerization and hydrolysis reactions. The petroleum industry uses anhydrous hydrogen fluoride primarily as a liquid catalyst for the alkylation of olefinic hydrocarbons to produce alkylate for increasing the octane number of gasoline.
The petroleum refining industry has always recognized the potential for hazard created by HF alkylation units. Accordingly, the industry has consistently ensured that a high level of safety is maintained by use of superior mechanical and metallurgical specifications, and operational practices in the design, construction and operation of these units. As a result, the HF alkylation process has enjoyed an almost unparalleled record of industrial safety. However, the industry has continued to seek enhancement of the intrinsic safety of these units to secure a higher level of potential operating safety and to guard against the consequences of an uncontrolled release of unit contents.
The potential magnitude of the risk inherent in operating an HF alkylation unit may be reduced by a number of qualitative methods that have been proposed for treating HF spills. The most common method is the use of a simple water drench system. Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Edition, Volume 1, page 655 reports that water the most common absorption liquid is used for removing acidic gases, especially if the last contact is with water of alkaline pH. However, because of the aerosol nature of an HF cloud in which the HF droplets are in the order of 0.1 micron and thus very small compared to droplets of water in a simple water drench, the water drench generally has difficulty in removing all the HF present in the cloud.
U.S. Pat. No. 4,210,460 relates to treating an HF liquid spill by applying to the spill a quantity of an aqueous solution of calcium acetate equal to at least seven times the estimated volume of the spill, and thereafter treating the spill with powdered magnesium oxide. The mixture is tested using a pH indicator such as bromothymol blue. After the mixture reaches a persistent blue color, indicating a safe state, the spill is cleaned up mechanically.
At the 1982 Hazardous Material Spills Conference, Edward C. Norman of National Foam System Inc reported the application of limestone and then CHF-784 foam (a proprietary composition) to the contents of a damaged tank emitting an HF cloud. An immediate reduction in fume evolution was apparent after the foam application.
Gordon K. Braley, at the proceedings of the 1980 National Conference on Control of Hazardous Material Spills, in Louisville, Ky. on May 15, 1980 reported the treatment of relatively small amounts of controlled liquid spills of anhydrous hydrogen fluoride with high molecular weight polymers including polyacrylamide, polymethyl methacrylate, and polyvinyl alcohol. These materials applied in the form of a bead polymer formed a skin over the spill preventing fuming of the liquid. Polyacrylamide was deemed the most effective skin-forming agent.
While these methods may be effective, it is desirable to provide a secondary line of protection to further enhance the operational safety of commercial operations using HF.